Frilled Shark Facts: A Strange and Fascinating Fish of the Deep
A Strange Fish of the Deep Ocean
The frilled shark is a fascinating and very strange fish that looks more like an eel than a shark. It has a wide head with a huge mouth and a long, slender body. Frilled sharks are sometimes called “living fossils” because they’re thought to be very similar to a prehistoric ancestor which lived eighty million years ago.
The mouth of the frilled shark is located at the end of the body instead of behind the tip of the snout as in most other sharks. The first pair of gill slits are especially long, extending from the sides of the body to underneath the throat. The gills have frilly structures on their edges, giving the shark its name.
Frilled sharks spend most of their time in deep water close to the sea bottom. Some people suggest that this shark is the basis of the sea serpent legends. It has the right shape to be mistaken for a sea serpent but it isn’t long enough, since it reaches a maximum length of only just under two meters (about six and a half feet).
Two living species of frilled sharks have been discovered. We know more about Chlamydoselachus anguineus, known simply as the “frilled shark”, than about the African frilled shark, Chlamydoselachus africana. Even so, there are lots of unanswered questions about the lives of these fish.
Video of a Sick or Injured Frilled Shark
The frilled shark is also known as the frill shark and the lizard shark. Its species name—anguineus—means "snake-like" in Latin.
Unusual Features of the Frilled Shark
Mouth and Teeth
The frilled shark has a big, wide, and flattened head dominated by a large mouth. The snout is rounded and the mouth has many rows of needle sharp teeth, each having three points. There are 300 teeth, which are arranged in 25 rows and point backwards.
The first gill slits are so long that they give the impression that the fish has been cut on its sides. The slits are often flared and the frills on the gills are red, increasing the impression of an injury. The frills sometimes look like a collar around the shark. There are six pairs of gill slits, unlike the five pairs found in most other sharks.
Body and Fins
The shark's elongated body is brown or grey. As in other sharks, the skin is rough and covered with small teeth-like structures called denticles. The small pectoral fins are located on the sides of the shark not far from its mouth, but the dorsal (back), pelvic, anal, and caudal (tail) fins are situated way back towards the rear of the body. There is only one dorsal fin, unlike the case in other sharks. The caudal fin is long and is sometimes said to resemble the wings (or "flights") on darts.
The Lateral Line
Many fish have a lateral line on each side of their body. The lateral line is a row of sense organs. It contains hair cells that are stimulated by movements and low-frequency vibrations in the water. The hair cells are said to be mechanoreceptive because they are sensitive to mechanical pressure.
The hair cells of a frilled shark's lateral line are located in a groove that is open to the ocean. This is an unusual feature in the world of sharks. In other sharks the lateral line is embedded in the skin and is connected to the outside world through pores.
A Swimming Frilled Shark
More Unusual Body Features of the Frilled Shark
- Unlike most sharks, frilled sharks have no nictitating membrane to cover their eyes. The nictitating membrane is a thin but tough membrane that acts like an eyelid and moves horizontally over the eye. A shark uses its nictitating membranes to protect its eyes during potentially dangerous situations, such as when lunging for a prey.
- There are a pair of thickened skin folds traveling along the shark's belly. The function of these folds is unknown. It's been suggested that they accommodate the expansion of the digestive tract after the ingestion of large prey.
- The huge liver contains a large quantity of low density oils and hydrocarbons (substances containing only hydrogen and carbon atoms), which help the shark to maintain its position in the water.
- The skeleton of the frilled shark is low in calcium, perhaps because the deep water in which it lives is poor in nutrients.
Unfortunately, the frilled shark is rarely seen alive. It's most often observed when it has been trapped in a fishing net and brought to the surface of the water after its death.
Lives of Frilled Sharks
The frilled shark has a wide range in both the Pacific and the Atlantic Oceans, but it's found in only scattered patches in these areas. It may live in water as deep as 1000 to 1500 meters, but it's usually located at depths of between 500 and 1000 meters. In some Japanese waters frilled sharks have been found in water between 50 and 200 meters deep.
By analyzing the stomach contents of captured frilled sharks, scientists have discovered that they eat squid, cuttlefish, octopuses, fish, and other sharks. Their feeding techniques are unknown, however. The frilled shark can open its mouth very wide and is said to be able to swallow prey that is half its size. One puzzle that needs to be answered is how the apparently slow moving shark can catch fast moving squid as well as slow moving ones. The long, thin shape of the fish may enable it to hunt in crevices and caves.
Scientists suspect that the shark generally strikes at its prey. It may draw smaller or weaker prey into its mouth by closing its gill slits and creating a partial vacuum that sucks up the animals. Though the mouth is huge, the structure of the jaws suggests that frilled sharks can't bite as hard as other sharks.
Sharks have internal fertilization. The male inserts sperm into the female with his claspers, which are located under his body by his pelvic fins.
The frilled shark is said to have an ovoviviparous method of reproduction, like many other sharks. The eggs are retained in the female's body instead of being laid. The embryos feed on the egg yolk inside the eggs. The eggs hatch inside the female's body and the pups are born live. Around six pups are born on average, although the number ranges from two to fifteen.
The frilled shark is believed to have a slow metabolism, since it lives mainly in cold, deep water. The development of the pups inside their mother is also slow. It's thought that a three and a half year gestation period may be needed, which would be the longest of any vertebrate. In Japanese waters, and perhaps in other areas too, frilled sharks breed at any time of the year. However, the long gestation period means that the shark has a low rate of reproduction.
Until quite recently, the frilled shark was classified as Near Threatened in the Red List of the IUCN (International Union for Conservation of Nature). This list categorizes animals according to their nearness to extinction. In 2016, the fish was reclassified and put in the "Least Concern" category. Hopefully this new classification is correct.
Unfortunately, current deepwater fishing techniques mean that frilled sharks are being caught as bycatch along with target species. This is worrying due to the long gestation period and small litter size of the fish.
Frilled Sharks in Captivity
The first video in this article shows a female frilled shark that was found swimming at the water's surface in Japan in 2007. She may have been ill or injured when she was found. She was taken to a marine park and unfortunately died a few hours later. This may have been due to a prior illness, to the relatively warm water in the marine park, or to a combination of these factors. Frilled sharks don't live long in captivity and therefore can't be protected or studied in aquariums or parks.
Scientists have been able to study dead frilled sharks but would love to know more about the lives of the living sharks. The fish don't seem to be dangerous to humans, unless someone gets cut by the sharp teeth while handling a dead animal. It would be a great shame to lose these creatures from the Earth, especially before we know much about them.
© 2012 Linda Crampton